Batwing LED with remote phosphor configuration

ABSTRACT

A lens is formed over one or more light-emitting devices disposed over a substrate. The lens includes a trench that circumferentially surrounds the one or more light-emitting devices. The trench is filled with a phosphor-containing material.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of application Ser. No. 14/584,009filed on Dec. 29, 2014, which is a continuation of U.S. application Ser.No. 14/248,491 filed on May 22, 2014, now U.S. Pat. No. 8,921,884, whichis a continuation of Ser. No. 13/946,007 filed on Jul. 19, 2013, nowU.S. Pat. No. 8,735,190, which is a divisional of application Ser. No.13/114,730 filed on May 24, 2011, now U.S. Pat. No. 8,497,519 for whichpriority is claimed under 35 U.S.C. §120; the entire contents of all ofwhich are hereby incorporated by reference.

BACKGROUND

1. Technical Field

The present disclosure relates generally to a lighting device and, moreparticularly, to light-emitting diode (LED) lighting device.

2. Description of the Related Art

A Light-Emitting Diode (LED), as used herein, is a semiconductor lightsource for generating a light at a specified wavelength or a range ofwavelengths. LEDs are traditionally used for indicator lamps, and areincreasingly used for displays. An LED emits light when a voltage isapplied across a p-n junction formed by oppositely doping semiconductorcompound layers. Different wavelengths of light can be generated usingdifferent materials by varying the bandgaps of the semiconductor layersand by fabricating an active layer within the p-n junction.

Traditionally, LEDs are made by growing light-emitting structures on agrowth substrate. The light-emitting structures along with theunderlying growth substrate are separated into individual LED dies. Atsome point before or after the separation, electrodes or conductive padsare added to the each of the LED dies to allow the conduction ofelectricity through the structure. LED dies are then packaged by addinga package substrate, optional phosphor material, and optics such as lensand reflectors to become an optical emitter.

Optical emitter specifications typically identify application-specificradiation patterns outputted by the optical emitter. A commonly usedbeam pattern is the batwing beam pattern for illuminating a flatsurface, in traffic signal applications, or in a backlighting unit for adisplay. The batwing beam pattern may be defined by having two roughlyequal peaks in a candela distribution plot with a valley between thepeaks at about 0 degrees.

Optical emitters are designed to meet these specifications. Whileexisting designs of optical emitters have been able to meet batwing beampattern requirements, they have not been entirely satisfactory in everyaspect. Reliable and more efficient designs that are easier tomanufacture continue to be sought.

SUMMARY OF THE DISCLOSURE

One aspect of the present disclosure involves an first LED die includinga upper surface, a lower surface, and a side surface arranged betweenthe upper surface to the lower surface; an transparent material coveringthe side surface and the upper surface; a phosphor surrounding the sidesurface; and a light-reflective element arranged on the transparentmaterial and having an outer thickness and a central thickness greaterthan the outer thickness.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart illustrating a method of fabricating an opticalemitter according to various aspects of the present disclosure.

FIGS. 2A to 2F illustrate cross-sectional views of an optical emitter atvarious stages of fabrication according to various embodiments.

FIGS. 3A to 3C illustrate cross section view and top view examples ofvarious embodiments of the present disclosure.

FIGS. 4A to 4C illustrate cross section view and top view examples ofvarious embodiments of the present disclosure.

FIGS. 5A to 5C illustrate cross section view and top view examples ofvarious embodiments of the present disclosure.

DETAILED DESCRIPTION OF THE EMBODIMENTS

It is understood that the following disclosure provides many differentembodiments, or examples, for implementing different features of variousembodiments. Specific examples of components and arrangements aredescribed below to simplify the present disclosure. These are, ofcourse, merely examples and are not intended to be limiting. Forexample, the formation of a feature over or on another feature in thedescription that follows may include embodiments in which the featureand the another feature are formed in direct contact, and may alsoinclude embodiments in which additional features may be formed betweenthe feature and the other features, such that the features may not be indirect contact. Of course, the description may specifically statewhether the features are directly in contact with each other. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Generally, an LED package, also referred to herein as an opticalemitter, includes an LED die attached to a package substrate, a layer ofphosphor material, and some optical components such as lenses and/orreflectors. The LED die is electrically connected to circuitry on thepackage substrate in a number of ways. One connection method known tothe inventors involves attaching the growth substrate portion of the dieto the package substrate, and forming electrode pads that are connectedto the p-type semiconductor layer and the n-type semiconductor layer inthe light-emitting structure on the die, and then bond wiring from theelectrode pads to contact pads on the package substrate. Anotherconnection method involves inverting the LED die and using solder bumpsto connect the electrode pads on the light-emitting structure directlyto the package substrate. This is known as a flip-chip package. Yetanother connection method involves using hybrid connectors. Onesemiconductor layer, for example the p-type layer, may be wired bondedto the package substrate while the other layer (n-type layer) may besoldered or metal bonded to the package substrate after removing thegrowth substrate.

The LED package may include one or more phosphor materials that areusually applied directly onto the LED die. Conventional methods ofapplying the one or more phosphor materials include spray-coating thephosphor materials in a concentrated viscous fluid medium, for example,liquid glue, onto the surface of the LED die through which the generatedlight must pass. As the viscous fluid sets or cures, the phosphormaterial becomes a part of the LED package. However, dosage anduniformity of a sprayed-on phosphor material is difficult to control.Further, the phosphor material is disposed in close proximity to the LEDdie and subjected to thermal cycling, which degrades the phosphormaterial over time reducing light output and changing color output.

Optical components such as reflectors and lenses are used to shape theradiation pattern, or beam pattern. Several optical components are oftenused to achieve a desired pattern, for example, a batwing beam pattern.A lens may be made of plastic, epoxy, or silicone and is attached to thepackage substrate by gluing its edge onto the package substrate.Usually, the lens is manufactured separately from the LED die and isavailable in specific sizes and shapes.

Conventional batwing optical emitters use two lenses to achieve thebatwing pattern. A first lens, or primary optics, is a transparent lensattached directly or formed directly on the LED die. The first lens isusually a semi-ellipsoid and functions primarily to extract as muchlight as possible from the LED die. A second lens, or secondary optics,is fitted and attached over the first lens and serves to shape the beampattern. Thus, using the methods known to the inventors, a variety ofbeam patterns may be generated by changing the second lens designwithout changing other portions of the LED package. Light thus generatedby the LED die may travel through a sapphire growth substrate, one ormore layers of phosphor material, through a first lens, possibly a gapbetween the first and the second lens, and finally through the secondlens for shaping the batwing pattern. The multiple interfaces can eachreduce the light output a small amount, and together, the light outputis reduced significantly from that of the LED dies.

The batwing optical emitter known to the inventor using the combinationof a primary and secondary optics suffers from several issues withmanufacturing, cost, and design. Because the second lens is madeseparately from the rest of the LED package, it is fitted over the firstlens during assembly. Alignment of these optical components affects theresulting beam pattern and thus the tolerance for the alignment is verylow. The low tolerance presents manufacturing issues and affects yield.Cost of the batwing optical emitter includes two lenses, which rendersthe batwing optical emitter more expensive than other optical emittersthat generate other beam patterns. As the LED dies becomes moreefficient and its dimensions reduce, the separately made second lens andthe alignment issue makes dimension reduction of the overall LED packagedifficult. While smaller second lens can be made, a smaller lensmagnifies mis-alignment issues and presents handling difficulties duringfinal assembly. Furthermore, the proximity of the phosphor to the LEDdies reduces device reliability and changes color over time.

An optical emitter in accordance with the present disclosure involvesonly one lens molded directly on one or more LED dies with the phosphormaterial not directly over the LED dies. Illustrated in FIG. 1 is aflowchart of a method 101 for fabricating an optical emitter inaccordance with various embodiments of the present disclosure. FIGS. 2Ato 2F are diagrammatic fragmentary cross-sectional side views of theoptical emitter during various fabrication stages in accordance with oneembodiment of the method 101 in FIG. 1. The optical emitter may be astandalone device or a part of an integrated circuit (IC) chip or systemon chip (SoC) that may include various passive and activemicroelectronic devices such as resistors, capacitors, inductors,diodes, metal-oxide semiconductor field effect transistors (MOSFET),complementary metal-oxide semiconductor (CMOS) transistors, bipolarjunction transistors (BJTs), laterally diffused MOS (LDMOS) transistors,high power MOS transistors, or other types of transistors. It isunderstood that FIGS. 2A to 2F have been simplified for a betterunderstanding of the inventive concepts of the present disclosure.Accordingly, it should be noted that additional processes may beprovided before, during, and after the method 101 of FIG. 1, and thatsome other processes may only be briefly described herein.

Referring to FIG. 1, the method. 101 begins with block 103 in which oneor more Light-Emitting Diode (LED) dies are attached to a packagesubstrate. FIG. 2 shows a cross-sectional view of a package substrate201. The package substrate 201 is a silicon substrate, a ceramicsubstrate, a gallium nitride substrate, a metal core printed circuitboard (MCPCB) or other package substrates used for packaging LEDs. Thepackage substrate may include metal pads 203 and through substrate vias205. Metal pads 203 and through substrate vias (TSVs) 205 are used onpackaging substrates in wafer level packaging to conduct electricityand/or heat. Though not necessary for the embodiments described in thisdisclosure, the use of metal pads and through substrate vias on asilicon substrate improves thermal and electrical conductivities.

FIG. 2B illustrates the LED dies 211 attached to the package substrate201. In certain embodiments, where the growth substrate side of the LEDdie is attached to the package substrate, the attachment may beperformed by simply gluing the LED die using any suitable conductive ornon-conductive glue, depending on whether the side of the LED die andthe package substrate to be attached are conductive and whetherisolation is required. In embodiments where the LED die side opposite ofthe growth substrate is attached to the package substrate, theattachment may include electrically connecting the LED die by bondingthe electrode pads on the LED to contact pads on the package substrate.This bonding may involve soldering or other metal bonding. In someembodiments, the growth substrate is removed and one side of the LED dieis bonded and electrically connected to the substrate. In this case theattaching may be accomplished using metal bonding such as eutecticbonding.

In one example, the LED dies are attached to the die by soldering. Tobond the LED die by soldering, a solder is printed on the packagesubstrate and reflowed while contacting the LED die. In another example,the LED dies are attached by being glued to the substrate using athermally conductive glue.

An LED die 211 includes a light-emitting structure (not shown) and oneor more electrode pads for electrically connecting to a packagesubstrate, the details of which are not shown in FIG. 2B. While thefollowing disclosure refers to an optical emitter with a blue LED, theconcepts describes herein could apply to other color LEDs as long as aphosphor is used to convert at least a portion of the light emitted fromthe LED to a different wavelength. The light-emitting structure has twodoped layers and a multiple quantum well layer between the doped layers.The doped layers are oppositely doped semiconductor layers. In someembodiments, a first doped layer includes an n-type gallium nitridematerial, and the second doped layer includes a p-type material. Inother embodiments, the first doped layer includes a p-type galliumnitride material, and the second doped layer includes an n-type galliumnitride material. The MQW layer includes alternating (or periodic)layers of active material, for example, gallium nitride and indiumgallium nitride. For example, in one embodiment, the MQW layer includesten layers of gallium nitride and ten layers of indium gallium nitride,where an indium gallium nitride layer is formed on a gallium nitridelayer, and another gallium nitride layer is formed on the indium galliumnitride layer, and so on and so forth.

The doped layers and the MQW layer are all formed by epitaxial growthprocesses. After the completion of the epitaxial growth process, a p-njunction (or a p-n diode) is essentially formed. When an electricalvoltage is applied between the doped layers, an electrical current flowsthrough the light-emitting structure, and the MQW layer emits light. Thecolor of the light emitted by the MQW layer associated with thewavelength of the emitted radiation, which may be tuned by varying thecomposition and structure of the materials that make up the MQW layer.The light-emitting structure may optionally include additional layerssuch as a buffer layer between the substrate and the first doped layer,a reflective layer, and an ohmic contact layer. A suitable buffer layermay be made of an undoped material of the first doped layer or othersimilar material. A light-reflecting layer may be a metal, such asaluminum, copper, titanium, silver, alloys of these, or combinationsthereof. An ohmic contact layer may be an indium tin oxide (ITO) layer,a titanium nitride layer, or a thin layer of other conductive materialthat is substantially transparent to the light emitted by the LED. Thelight reflecting layer and ohmic contact layer may be formed by aphysical vapor deposition (PVD) process, a chemical vapor deposition(CVD), or other deposition processes.

After the LED die is attached to the substrate, the LED die iselectrically connected to the package substrate in operation 105 ofFIG. 1. At least two electrical connections are made, one each to thep-type and n-type doped layers. In some cases, two electricalconnections are made to the p-type layer for current spreading purposes.As discussed, the electrical connection may involve wire bonding,soldering, metal bonding, or a combination of these. FIG. 2B furtherillustrates wire bonds 213 between the LED dies 211 and metal pads 203.The wire bonds 213 connect electrodes on the LEDs the metal pads 203,which is electrically connected to terminals on the back side of thepackage substrate 201 through the TSVs 205. Although the FIG. 2Billustrate a horizontal package, the LED dies may be attached to thepackage substrate in a number of ways, including vertical packagingusing only one wire bond or flip chip packaging using no wires. Becausethe electrical connection 213 may take a variety of forms, the structureshown in FIG. 2B is illustrative only—the electrical connections 213need not be a wire bond.

Referring back to FIG. 1, at operation 107 a lens is molded over the LEDdies and the package substrate. The lens includes a circumferentialtrench. The lens may be formed by injection molding or compressionmolding. A variety of materials may be used as the lens. Suitablematerials have a high optical permissivity (transparency), a viscositysuitable for molding, appropriate adhesion to the package substrate, andgood thermal conductivity and stability (i.e., do not degrade or changecolor during thermal cycling). Example materials include silicone,epoxy, certain polymers, resins and plastics including Poly(methylmethacrylate) (PMMA). Suitable materials are flowable for molding intothe lens and can be cured into a defined shape. Some suitable materialsmay have thermal expansion coefficients that are similar to that of thepackage substrate and/or can absorb stress caused by a difference in thethermal expansion during thermal cycling. Examples of suitable lensmaterials include Shin-Etsu's line of SCR and KER silicone resins andrubber materials and Dow Cornings' various lines of silicon gels,elastomers, and silicone resins. As understood, a manufacturer in theindustry can adjust the refractive index of the lens material as acustomer specifies. Thus, one skilled in the art can select a suitablelens material based on suitable material properties other than therefractive index first, then specify the refractive index within a rangethat can be supplied by the manufacturer.

In certain embodiments, a compression molding method is used as shown inFIG. 2C. A lens precursor material 221 is dispensed over the LED diesand the package substrate 201 and then a lens mold 223 is placed overlens precursor material 221. The lens mold 223 includes circumferentialtrench 225 and may include one or more openings for excess lens materialand air to escape the mold 223 as the mold 223 is compressed against thepackage substrate 201. The position and number of openings on the lensmold 223 depends on the process conditions and the material propertiesinvolved. A number of openings may be used and the openings may belocated at different places. While FIG. 2C illustrate one lens cavityplaced over two LED dies, the lens mold 223 may include multiple moldcavities that would fit over a package substrate 201 having many LEDdies attached thereon to form lenses for a number of packages at thesame time. The package substrate 201 may include alignment marks betweenindividual LED dies to ensure that the lens cavities are placedaccurately over the LED dies.

To ensure a good fill, the gas inside the lens cavity may be evacuatedthrough one or more openings. Alternatively, this operation is performedin a vacuum environment, in which the instant openings may be notrequired. The lens precursor material/glue 221 may be heated or underpressure. The lens precursor material 221 fills the lens cavity to formthe lens when the mold 223 is pressed against the package substrate 201.

The lens precursor material 221 is cured to set so that it retains itsshape and adheres to the package substrate 201 and LED die as shown.Radiation or other energy may be applied to the lens mold 223, whichallows the radiation the pass through. The radiation may be anultraviolet (UV) radiation, thermal radiation (infrared), microwave, oranother radiation that can cure the lens glue. Glue materials that cureunder UV light or under heat application are commercially available. Insome instances, curing may be accomplished by only thermal energy, whichneed not be applied in the form of radiation. Conductive heat energy maybe applied through the package substrate 201 or through heating of thelens mold 223.

After the lens has cured, the lens mold 223 may be removed, as shown inFIG. 2D. The lens mold 223 is removed so as not to remove the lens 231from the package substrate 201. In one embodiment, some gas can be addedvia one or all of the mold openings to help separate the lens 231 fromthe lens mold 223. Other techniques include changing the temperature ofeither the lens molded 223 or the lens mold 223 such that a temperaturedifference exists or using a removal template in the lens mold 223. Inanother embodiment, the circumferential trenches 225 are made to havedifferent trench widths. The trench may be narrower at the bottom andwider at the top so that the lens mold 223 is easier to remove.

The circumferential trench 233 is thus formed in the lens 231. Note thatFIG. 2D shows neighboring circumferential trenches 235 and 237 formed bythe same mold. These neighboring circumferential trenches 235 and 237belong to neighboring optical emitters. Eventually, the packagesubstrate 201 will be diced into individual optical emitters at thelocation between the circumferential trenches, for example, betweentrenches 233 and 237, through the lens material to form individualoptical emitters.

Referring back to FIG. 1, in operation 109 the circumferential trenchesare filled with a phosphor material. The phosphor material may be filledby dispensing or injecting the phosphor material into thecircumferential trenches, as shown in FIG. 2E. The dispensing may beaccomplished by printing a viscous liquid containing the phosphor overthe lens material, and flowing the liquid into the trenches byvibration, either via physical movement of the package substrate 201 orsonic/ultrasonic waves. The dispensing may also be accomplished bysubmerging the entire partially fabricated package into a liquid mediumcontaining the phosphor material. The injecting may be accomplished bytracing the trench with an injection gun or pen. An entirecircumferential trench may be injected by using injection guns withoutput ports having the same shape as the circumferential trench.Further, the circumferential trenches may be filled by a spin coatingprocess where excess material is spun off the surface of the lens. Oneskilled in the art would be able to select the right material withphosphor to form the phosphor material so that the trenches can beproperly filled based on the filling technique to be used.

After the phosphor material is applied to the circumferential trench, itis solidified into a circumferential cylinder, shown as 241 in FIG. 2E.Phosphor may be mixed with silicone, epoxy, polymers, resins, siliconeresin and plastics including Poly(methyl methacrylate) (PMMA). Thematerial is preferably selected to have similar thermal expansioncoefficients as the lens so as to minimize thermal cycling inducedstress between the two materials. Of course, the same base material maybe used—the only difference being the addition of phosphor. Depending onthe material properties of the mixture, the phosphor material may besolidified by curing with radiation or heat and by setting and allowingchemical reactions to form a matrix. The phosphor cylinder is thenembedded in the lens.

If the circumferential trench has varying widths, then thecircumferential cylinder formed also has varying thicknesses. This wallof phosphor serves to change the wavelength of LED emitted light andreflected light so that a light of different color from what was emittedis perceived outside of the optical emitter. The thickness variance maydepend on the expected light at different locations of the cylinder tocreate a uniform color distribution. For example, where more reflectedlight is expected, the cylinder wall may be thicker so the lightconverted by the phosphor remains the same ratio regardless of the angleof perception. This phosphor cylinder 241 may also be used inconjunction with another phosphor layer, for example, another phosphorcylinder concentric to the first one (243 and 245) or a phosphor layerapplied directly to the LED dies to create a variety of colors, forexample, white light. To create white light, when only one phosphorcylinder is used, the phosphor may be a phosphor that generates yellowlight when excited by a blue light. When two phosphor layers are used,one phosphor layer may be a green phosphor and another may be a redphosphor. In other embodiments, phosphor cylinders 243 and 245 areseparate cylinders belonging to different optical emitters.

In some embodiments, the curing for the phosphor cylinder and the lensmay occur sequentially or together. The lens may be formed and set witha soft cure so as to retain its shape. Then the phosphor material may beadded to the circumferential trench. The two materials may be curedtogether in a “hard bake” to finalize the solidification process.

In other embodiments, the lens may be formed and cured completely beforethe phosphor material is added. The phosphor cylinder may be designed tobe softer than the lens material. Then during the thermal cycling thephosphor cylinder may absorb some of the thermal expansion stresseswhich reduces the chance that the thermal cycling stresses delaminatesthe lens from the package substrate.

Referring back to FIG. 1, after the lens and the phosphor cylinder areformed, a top surface of the lens may be optionally coated with areflective material in operation 111. As noted above, the requiredreflectivity of the surface coating material depends on the batwing beampattern requirements and a variety of coating material may be used. Thesurface coating material may be dispensed, sprayed, spun, or otherwisedeposited on the lens top surface. An example would be to use a gelcontaining reflective additives, for example, a silicon gel, dispensedonto the top surface of the lens. Additives may include metal particlessuch as silver or other metals, some metal oxide such as titanium oxide,zinc oxide, and zirconium oxide. Other highly reflective additives maybe used. Examples of other highly reflective coatings include dielectricfilms tuned to reflect the specific wavelengths of light emitted by theLED die. In some embodiments, the surface coating selected reflects morethan 80% of the incident light, about 90% of the incident light, or morethan 90% of the incident light. In some instances the surface coatingmerely coats a portion of top surface. In other instances the surfacecoating may coat the entire top surface. FIG. 2F illustrate a reflector251 coating on a portion of the lens.

In other embodiments, the reflective coating is not used. The lens maybe shaped such that light reaching the top surface from the LED die ismostly reflected off the surface as total internal reflection (TIR). TIRis an optical phenomenon that occurs when a ray of light strikes aboundary between two medium at an angle larger than a particularcritical angle with respect to the normal to the surface. At this largerangle, if the refractive index is lower on the other side of theboundary, no light can pass through and all of the light is reflected.The critical angle is the angle of incidence above which the totalinternal reflection occurs. If the angle of incidence is greater (i.e.,the ray is closer to being parallel to the boundary) than the criticalangle—the angle of incidence at which light is refracted such that ittravels along the boundary—then the light will stop crossing theboundary altogether and instead be totally reflected back internally.The top lens surface in accordance with various embodiments of thepresent disclosure has a surface that renders most of the angle ofincidence greater than the critical angle. Because the refractive indexon the other side of the top surface is lower (for example, air has arefractive index of about 1) than that of the lens (for example, siliconmolding has refractive indices of about 1.4 to 1.55), most of the lightfrom the LED may be reflected as TIR. A combination of surface coatingand lens shape design may be used to ensure that most of the lightemitted by the LED dies is reflected from the top surface.

Referring back to FIG. 1, the package substrate 201 may be diced into anumber of optical emitters in operation 113. As shown in FIG. 2F, theoptical emitter is separated from its neighbors outside of the phosphorcylinder. The package substrate 201 may be diced using mechanical meanssuch as sawing or cutting. The package substrate 201 may also be dicedusing radiation energy, such as laser. The use of laser allows anon-linear cut to be used. For example, the optical emitters may have around base instead of a rectangular base.

The optical emitter according to various embodiments of the presentdisclosure applies to having only one LED die 303 as well as several LEDdies 303. The LED dies 303 may be arranged in a linear array, in arectangular array, or in a circle or other shapes. FIGS. 3A to 3Cillustrate a number of embodiments. FIG. 3A is a cross section view ofFIG. 3B or 3C, at a 45 degree angle through a center of the opticalemitter. The embodiments of FIGS. 3A to 3C include no reflective coatingon the top surface of the lens 301. In these embodiments, four LED dies303 are mounted on the substrate 305. In FIG. 3B, each die 303 has aside closest to the center of the optical emitter. In FIG. 3C, each die303 has a corner closest to the center of the optical emitter. Theplacement of the dies 303 depends on the profile of the lens 301 tocause TIR. Note that the package substrate 305 for the optical emittermay be a rectangle or square as shown in FIG. 3B; or round or oval asshown in FIG. 3C. The phosphor circumferential cylinder 311 may also beround or oval depending on the shape and placement of the LED dies 303and the lens 301 shape. In a top view, the lens 301 has a circular oroval shape. The shape may be achieved by the mold when the lens 301 isformed. The shape may also be formed by subsequent cutting or etching.

FIGS. 4A to 4C illustrate a number of other embodiments. FIG. 4A is across section view of FIG. 4B or 4C, at a 45 degree angle through acenter of the optical emitter. The embodiments of FIGS. 4A to 4Cincludes reflective coating 407 on a portion of the top surface of thelens 401. The portion may be a center portion. The coating 407 maypartially fill a cavity as shown in FIG. 4A, or may be applied as a thinlayer. In these embodiments, four LED dies 403 are mounted on thesubstrate 405. In FIG. 4B, each die 403 has a side closest to the centerof the optical emitter. In FIG. 4C, each die 403 has a corner closest tothe center of the optical emitter. The reflective coating 407, the shapeof the lens 401, and placement of the dies 403 together cause TIR offthe top surface of the lens. Note that the package substrate 405 for theoptical emitter may be a rectangle or square as shown in FIG. 4B; orround or oval as shown in FIG. 4C.

FIGS. 5A to 5C illustrate yet a number of other embodiments. FIG. 5A isa cross section view of FIG. 5B or 5C, at a 45 degree angle through acenter of the optical emitter. The embodiments of FIGS. 5A to 5C includereflective coating 507 on a portion of the top surface of the lens 501.The portion may be a center portion. The coating 505 may fill a cavityas shown in FIG. 5A, or may be applied as a thin layer over the entiretop surface of the lens 501. In these embodiments, four LED dies 503 aremounted on the substrate 505. In FIG. 5B, each die 503 has a sideclosest to the center of the optical emitter. In FIG. 5C, each die 503has a corner closest to the center of the optical emitter. Thereflective coating 505 causes TIR off the top surface of all of thelights generated by the LED dies 503 to exit the optical emitter fromthe sides. Note that the package substrate 505 for the optical emittermay be a rectangle or square as shown in FIG. 5B; or round or oval asshown in FIG. 5C.

In other embodiments of the present disclosure, a different number ofLED dies are used. For example, three LED dies may be arranged to formvertices of an equilateral triangle. In another embodiment, five LEDdies are arranged to form two rows—one row of two LED dies and one rowof three LED dies. In each of these multiple LED die configurations, onelens is formed over the LED dies.

The foregoing has outlined features of several embodiments so that thoseskilled in the art may better understand the detailed description thatfollows. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein. Itis understood, however, that these advantages are not meant to belimiting, and that other embodiments may offer other advantages. Thoseskilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions andalterations herein without departing from the spirit and scope of thepresent disclosure.

The invention claimed is:
 1. A lighting device, comprising: a first LEDdie comprising a upper surface, a lower surface, and a side surfacearranged between the upper surface and the lower surface; a phosphorsurrounding the side surface; a transparent material devoid of thephosphor, and covering the side surface and the upper surface; and alight-reflective element arranged on the transparent material and havingan outer thickness and a central thickness greater than the outerthickness, wherein the light-reflective element covers only a portion ofa top surface of the transparent material.
 2. The lighting device ofclaim 1, wherein the light-reflective element comprises a convex portionand a plane opposite to the convex portion.
 3. The lighting device ofclaim 1, wherein the light-reflective element directly contacts thetransparent material.
 4. The lighting device of claim 1, wherein thelight-reflective element comprises a metal or a metal oxide.
 5. Thelighting device of claim 1, wherein the transparent material has a topcontour substantially corresponding to a bottom contour of thelight-reflective material.
 6. The lighting device of claim 1, whereinthe transparent material has a ring shape in a top sectional view of thelighting device.
 7. The lighting device of claim 1, wherein thetransparent material comprises a trench.
 8. The lighting device of claim1, wherein the phosphor is separated from the first LED die by thetransparent material.
 9. The lighting device of claim 1, wherein thephosphor is directly connected to the transparent material.
 10. Thelighting device of claim 1, wherein the phosphor has a tubular shape.11. The lighting device of claim 1, further comprising a second LED dienear the first LED die.
 12. The lighting device of claim 11, wherein thelight-reflective element comprises a convex portion corresponding to aposition between the first LED die and the second LED die.
 13. Thelighting device of claim 11, wherein the first LED die and the secondLED die are electrically connected in series.
 14. The lighting device ofclaim 7, wherein the trench has a close loop configuration surroundingthe first LED die.
 15. The lighting device of claim 1, wherein thephosphor has a layer having a first height smaller than a maximumthickness of the transparent material in a sectional view.
 16. Thelighting device of claim 1, wherein the first LED die and thelight-reflective element are not overlapped with each other in a topview.
 17. A lighting device, comprising: a first LED die comprising aupper surface, a lower surface, and a side surface arranged between theupper surface and the lower surface; a phosphor surrounding the sidesurface; an transparent material covering the side surface and the uppersurface; a light-reflective element arranged on the transparentmaterial, and having an outer thickness and a central thickness greaterthan the outer thickness, wherein the light-reflective element coversonly a portion of a top surface of the transparent material.
 18. Alighting device, comprising: a first LED die comprising a upper surface,a lower surface, and a side surface arranged between the upper surfaceand the lower surface; a phosphor surrounding the side surface; antransparent material covering the side surface and the upper surface; alight-reflective element arranged on the transparent material, having anouter thickness and a central thickness greater than the outerthickness, and having a top plane substantially parallel to the uppersurface.